The present invention relates to apparatus for freeze-drying products, of the kind comprising an enclosure within which are placed superposed shelves provided with cooling and heating means and carrying vessels for containing the said products.
It is known that freeze-drying is a method for eliminating water from the structure of organic or inorganic substances, in particular from products of the nutritional and pharmaceutical types among others, and which essentially consists in a freezing operation followed by a sublimating operation under vacuum.
Freeze-drying apparatus known at present comprise either two separate enclosures one of which is utilised for freezing and the other for sublimation, the latter being evacuable, or a single enclosure in which the two freezing and sublimating operations are performed consecutively and which may be placed under vacuum for this second operation.
Although apparatus of this second kind forms an obvious simplification compared to the first by reducing bulk and control operations, it still has grave disadvantages: the shelves must be chilled and heated alternately to produce freezing and sublimation. This leads to a substantial power wastage as well as to an appreciable loss of time, since it is necessary to wait for the temperature inversion to have taken place within the shelves.